Well gravelling tool

ABSTRACT

A well gravelling tool for operative engagement with a drill pipe string for use in the conveyance, positioning and gravel packing of a tubular member, e.g., a perforated tubular element, liner, screen, or the like, within a well via use of a watergravel slurry passed downward through the drill pipe string to the well bottom. The tool comprises a pair of concentric tubular members, an outer large diameter tubular member, and an inner small diameter tubular member, between which an annulus is formed, which annulus is in open communication with the passageway leading to the surface through the drill pipe string. The inner small diameter tubular member opens through the wall of the larger diameter tubular member to the exterior, and the upper portion thereof is closed to the annular passageway. The lower extremity of the inner small diameter tubular member is provided with a check valve which permits ascent of liquid through the opening through the inner small diameter tubular member, but not downward flow. A tubular segment is located adjacent the check valve and on the lower extremity of the inner small diameter tubular member for operative engagement with the tubular member to be conveyed, positioned and packed within the well bottom. In operation, a water-gravel slurry is passed downwardly through the drill pipe string, the annulus between the concentrically mounted large and small diameter tubular members, and gravel is dispersed about the tubular element positioned at the bottom of the well. (Water flows through the gravel packing, into the tubular elements, and via the check valve through the small diameter tubular member and into the annulus located between the well casing and external wall of the pipe string to the surface.

United States Patent [191 Jordan [451 Sept. 16, 1975 WELL GRAVELLINGTOOL [75] Inventor: Glen L. Jordan, Houma, La.

[73] Assignees: Ernest R. Jordan; Jack D. McCartney, Jr.; James C.McGueyer, all of Houma, La.

[22] Filed: Apr. 15, 1974 [21] Appl. No.: 460,750

Primary Exuminer.lames A. Leppink Attorney, Agent, or FirmLlewellyn A.Proctor [57] ABSTRACT A well gravelling tool for operative engagementwith a drill pipe string for use in the conveyance, positioning andgravel packing of a tubular member, e.g., a perforated tubular element,liner, screen, or the like, within a well via use of a water-gravelslurry passed downward through the-drill pipe string to the well bottom.The tool comprises a pair of concentric tubular members, an outer largediameter tubular member, and an inner small diameter tubular member,between which an annulus is formed, which annulus is in opencommunication with the passageway leading to the surface through thedrill pipe string. The inner small diameter tubular member opens throughthe wall of the larger diameter tubular member to the exterior, and theupper portion thereof is closed to the annular passageway. The lowerextremity of the inner small diameter tubular member is provided with acheck valve which permits ascent of liquid through the opening throughthe inner small diameter tubular member, but not downward flow. Atubular segment is located adjacent the check valve and on the lowerextremity of the inner small diameter tubular member for operativeengagement with the tubular member to be conveyed, positioned and packedwithin the well bottom. In operation, a water-gravel slurry is passeddownwardly through the drill pipe string, the annulus between theconcentrically mounted large and small diameter tubular members, andgravel is dispersed about the tubular element positioned at the bottomof the well. (Water flows through the gravel packing, into the tubularelements, and via the check valve through the small diameter tubularmember and into the annulus located between the well casing and externalwall of the pipe string to the surface.)

10 Claims, 4 Drawing Figures Kai WELL GRAVELLING TOOL ln drilling deepwells, it is conventional to position tubular shaped members, includingblank pipes, foram inous liners, sand screens, and the like, within wellbores at the locations of producing sand stratums. Typically, tubularshaped members, or blank pipes, are alternately placed with the sandscreens, in series, one atop the other. Gravel is placed about suchmembers to prevent caving, spillage, and influx of sand into the well.

Several types of gravel pack apparatus, or gravel pack systems, areknown to the art. All are structured to provide means for depositinggravel about the outer face of the tubular elements, e.g., the screen orforami nous liner, while precluding deposition of gravel inside theliner. In certain systems, the gravel is contained within bailers, orcontainers, let down upon wire or cable from the surface to the wellbottom. For example, apparatus of such type is described in US. Pat. No.2,140,072 granted to R. L. Chenault. A cable conveyed container, forretention of the gravel, is provided with valve means adjacent thebottom of the container. The valve is constructed so that the gravelfilled container is normally closed to retain the gravel, but is adaptedto open on contact of the bottom of the container with the liner aboutwhich gravel is to be packed. Another apparatus of such generalcharacter is described by US. Pat. No. 3,182,723 granted to W. K. Layne,Sr. This device is also characterized as a cableconveyed bailer beneathwhich is suspended a smaller diameter double-end conical shaped baffledevice, a lower end of which is to contact and block off the liner tothe flow of solids while the upper end is employed to better distributethe gravel upon its release from the bailer. The bailer is provided witha frangible disk upon which the gravel rests, and adjacent thereto isprovided a remotely controlled explosive cap. The explosive cap is setoff from the surface to rupture the frangible disk and release gravelfrom the bailer. While these and other such devices have proven usefulfor the purposes intended, all are too complex. One major difficulty,particularly with the bailer type devices, is that considerable time isrequired for the many trips" down the well bore. The necessity of themany incremental releases of gravel and the great number of repetitivesteps involved in gravel packing is unduly burdensome. Moreover, it isnecessary to make very accurate and exact calculations in discharginggravel into a well for there is no way to return excess gravel resultingfrom overfills. Less complex devices, capable of more rapid operation,but yet capable of a high degree of precision by ordinary operatinglabor, are needed.

In another type of well gravelling system, such as the hydraulic packingsystem described by US. Pat. No. 2,372,461 granted to L. C. Uren, thelower portion of the well bore is capped off, the top of the liner istemporarily plugged, and a gravel slurry is pumped downwardly from thesurface through a string of tubing, which encloses the liner. The slurryis passed downwardly, through the annular opening between the tubing andthe liner, and out the lower terminal end of the tubing. The gravelsettles within the cavity or annular space between the well wall and theliner, and liquid ascends through the annulus between the well wall andthe said tubing to the surface.

The well gravelling tool described in D. C. Smiths U.S. Pat. No.3,630,277 has proven particularly suitable for use in gravel packing.The well gravelling tool described therein comprises a pair ofconcentric members, a smaller diameter member mounted within a largerdiameter tubular member, providing an annular opening which iscommunicated to the opening through the drill pipe string. The drillpipe string and well gravelling tool are operatively engageable, e.g.,via threadable connections one member with the other, and the wellgravelling tool, in turn, is engageable, e.g., via threadableconnection, of opposite cast, with a tubular member located within thebottom of the well to seal the interior of the latter from entry offluid or gravel. Gravel is discharged downwardly from the surfacethrough the drill pipe string and well gravelling tool to fill theannulus of the well outside the tubular element. Water, in a seconddiscrete step, is forced down into the well to pack the gravel and pickup any excess which is returned to the surface with the water whichascends through the well gravelling tool and drill pipe string. Whereasthis tool has proven admirably suitable for packing wells, the presentinvention is nonetheless an improvement thereover.

Accordingly, the primary object of the present invention is to provide anew and novel well gravelling tool, characterized particularly as onewherein the grave] is dispersed as a slurry, and the gravel thereofpacked around the tubular element located in the well bottom, whilesimultaneously the water is returned to the surface.

A further object is to provide a new and novel well gravelling tool ofsimplified construction, one which is easily serviced, easily operated,and capable of packing wells with considerable economy.

These objects and others are achieved in accordance with the presentinvention comprising a well gravelling tool for use in combination witha drill pipe string. The well gravelling tool is secured upon, andoperatively engaged with, a drill pipe string, and so positioned on thedrill pipe string it can be used to lower a tubular member, e.g., aliner or screen, into a well or well casing wherein the'tubular membercan be attached to other tubular members of a series positioned in thewell bottom and packed in the bottom of the well within an oil producingstratum to provide a path for oil flow from the formation through thepack and the series of aligned tubular members into the drill string. Inpacking the gravel about the tubular member, a watergravel slurry ispassed downwardly from the surface via the drill pipe string through afirst conduit within the well gravelling tool, and water returned fromthe bottom of the well to the surface via a second conduit within thewell gravelling tool, the water after passage through the wellgravelling tool ascending within an annulus between the productiontubing and the outer surface of the drill pipe string.

The well gravelling tool is comprised generally of a pair of concentrictubular members, an outer tubular member of relatively large diameterinside which the inner smaller diameter tubular member is mounted. Theupper end of the inner smaller diameter tubular member is opened throughthe wall of the outer tubular member to the exterior, while being closedto the tubular opening through the outer tubular member. The relativediameters of the outer and inner tubular members are such as to providean annular opening which extends from the top of the outer tubularmember downwardly therethrough, the annulus forming a separate anddistinct passageway from that which extends through the tubular openingwithin the inner tubular member. The lower terminal end of the innertubular member is preferably extended beyond the lower terminal end ofthe annular passageway and, preferably also, a check valve mountedthereon closes the tubular opening of the inner tubular member to flowin a downward direction, but leaves the tubular opening open to upwardflow. The lowermost portion of the inner tubular member, or at alocation below the check valve, there is provided a tubular element foroperative engagement with a tubular member to be positioned within thewell. In its most preferred form, the tubular element is provided withan externally threaded lower end which permits coupling of the lower endof the tool via a threaded union to a tubular member of the type to bepacked within the well bottom. In a preferred embodiment also, the upperterminal end of the tool com prising the outer tubular member, generallyof reduced cross-section, is externally threaded for threadableengagement, e.g., via a union connection, to a drill pipe of a drillpipe string.

In operatively positioning the tool for service, the upper end of thetool is operatively engaged to a drill pipe string, and the lower end ofthe tool to a tubular member to be packed in the well. After the timethat the tubular member has been positioned at the bottom of the welland is ready for packing, a preselected amount of gravel contained in awater-gravel slurry is passed downwardly under pressure through thedrill pipe string and through the annular passageway through the toolsuch that the gravel is spread around the tubular element and packed.The water. which is separated from the slurry, simultaneously entersinto the path formed by the train of packed tubular members and ascendstherethrough, through the check valve and into the tubular Opening ofthe inner tubular member. and exits near the upper end of the tool intothe annulus between the production tubing, the outer wall of the outertubular member and drill pipes and ascends to the surface.

These and other features and advantages will be better understood byreference to the following detailed description and to the accompanyingdrawings to which reference is made in the description. Subscripts areused to denote the sub-components ofa larger subassembly of the tool.Subscripts are dropped in the written description, where the referenceis intended in generic sense.

Referring to the drawings:

FIG. I is a section elevation view depicting a preferred well gravellingtool.

FIG. 2 is a plan view, taken along section 2-2 of FIG. 1, depicting astructural detail of the preferred well gravelling tool.

FIGS. 3 and 4 are elevation views in partial section illustrating themanner in which the well gravelling tool is mounted on a drill pipestring and its interrelationship with a tubular member which has beenlocated at the bottom of a well, inclusive of the technique of using awater-gravel slurry in dispersing and packing gravel around the tubularmember. For convenience, since both occur simultaneously, the path ofdistribution of the gravel is depicted in the first figure of thisseries, and the path offlow for water removal in the latter figure.

Referring to FIG. I, there is shown a preferred gravel packing apparatusor well gravelling tool 10 which, in operative engagement with a drillpipe string, can be used for gravel packing a well. The well gravellingtool 10 is constituted generally of an outer tubular casing 1 l, aportion of which is of relatively large diameter, an inner tubulareasing I2 of relatively small diameter concentrically mounted within theouter tubular mem ber 11, preferably a one-way flow valve 14 mountedupon a lower terminal end ofa projecting portion of the inner tubularcasing 12, and a tubular fitting 15 fitted on the lower end of the valve14.

The outer tubular member lll can be made as a unitary tubular member, orfitted together from a plurality of tubular segments of uniform outsidediameter, i.e., segments 11 and 11 as depicted in the drawings. Lowertubular segment 11 is thus adjoined to or threadably engaged to uppersegment 11 via internal threads 11 which mate with external threads 11on the smaller diameter projecting lower end of tubular segment lll ofouter tubular segment 11. The extreme lower end of tubular member 11 (ortubular segment 11 is, in preferred embodiments, provided with anelastic seal 13 of tubular shape which fits upon a lip located at theterminal end of the tubular member 11. The seal 13, in turn, fitsagainst the surrounding production tubing ofa producing well to closeand seal the annulus formed between the external wall which forms outertubular member 11 and the internal wall which forms the productiontubing. The top of the inner tubular member 12 is open to the exteriorof the outer tubular member via an opening, or openings 12,, 12 throughthe wall of outer tubular member 11 at locationsjust below theexternally threaded upper reduced segment ll, thereof from which thetool can be adjoined. e.g., via an appropriate union to a pipe of adrill pipe string. The inner tubular member 12, as stated, is fittedconcentrically within the larger diameter outer tubular member lll andsufficient clearance is provided between the external wall of innermember 12 and the inside wall of outer member 11 to provide an annularpassageway which, despite the minor obstructions offered by the wallsegments of inner member 12 at the location of openings 12 12 leads fromthe opening at the very top or apex of outer tubular member 11 (atlocation 11, to the opening at the bottom of outer tubular member 11 (atthe location of elastic seal 13).

A check valve, or oneway flow valve 14, in accordance with a preferredoptional feature, is operatively secured upon and adjoined to the lowerprojecting tapered end of inner tubular member 12. The valve 14 isconstituted of a valve body comprising adjoined tubular segments 14,, 14within which is fitted a spring biased gate opening I4 The valve 14 isthus constituted of an upper body comprising tubular segment 14,provided with an externally threaded lower shank portion 14 The insideof the upper larger portion 14 is tapped and internally threaded, byvirtue of which the valve 14 can be threadably engaged upon and upon andsecured to an externally threaded portion of the lower (reduceddiameter) terminal end of inner member 12. The lower body portion of thevalve 14 is constituted ofa tubular member 14 the upper internal portionof which is threaded for mating or threadable engagement with theexternally threaded lower shank portion 14 of upper body portion 14 ofvalve 14. The members are sealed together via a protective O-ring 9which is seated between contacting surfaces. The lower body portion ofvalve 14, i.e., tubular member 14 is partially enclosed by a bottomwall, but contains an externally threaded tubular projection which isthreadably engaged with, and secured upon, a tubular fitting 15. A gate14;, provided with a plurality of openings 14 A, 14 leading into a mainopening 14 is seated within the lower portion of tubular member 14 and aprojected upper portion thereof is fitted within a helical spring 14such that its lower end 14 can be seated and unseated within the channelwhich leads into the axial opening through inner tubular member 12. Theupper end of tubular fitting 15, this end of which is frustoconic shapedwith its tapered end upward, is internally threaded and threadablyengaged with the lower externally threaded projection of valve 14, andthe lower end thereof is externally threaded for threadable engagementwith a tubular element such as located at the bottom of a well to bepacked.

The external side wall of the tubular fitting 15 is preferably serrated,or ridged by a plurality of even spaced, longitudinally orientedgrooves, in this instance four in number, 15,, 15 15 15 as shown byreference to FIG. 2. The function of these grooves is to prevent orsuppress bridging of particles between the outer walls of the tubularfitting l5 and the inside walls of the well casing.

Referring to FIGS. 3 and 4, there is shown a borehole or well 16 whichextends through the earth B into a producing formation A from which oilis to be taken.

A perforated metal casing is located within and aligns the borehole orwell 16 to prevent cave-ins such as can occur at locations wherein thewell passes through loose or weak formations of earth. In packing a well16, a perforated liner or screen 17 is lowered via the drill pipe stringthrough the casing and substantially concentrically aligned therewith,and gravel is packed within the annulus between the external surface ofthe screen 17 and the internal side of the wall of the casing.

In the operation of packing a well 16, the tool 10 is used in thefollowing manner: The tool 10, at the surface, is secured via its upperthreaded end 11 to the lower end ofa drill pipe 18 of a drill pipestring. These members 10, 18 are preferably threadably secured each tothe other via threadable engagement to a union connection 19, righthanded threads generally being employed to couple these memberstogether. A screen 17 is next secured upon the lower end of the tool 10via connection to the tubular fitting 15. The members 15, 17 arepreferably threadably secured one to the other via threadable engagementto a union connection 20. Left handed threads are employed to couplethese members 15, 17 one to the other. The coupled members, whichinclude the pipe. 18 of the drill pipe string, the tool 10 (with itscomponent parts), and the screen 17, are then lowered through productiontubing 8 into the well 16, as shown by either of FIGS. 3 or 4, until thelower end of screen 17 contacts a union (not shown) mounted on the upperend of a previously attached pipe blank (not shown) at which time theassembly is rotated in counterclockwise direction to produce threadableengagement and secure the screen 17 upon the pipe blank.

A watengravel slurry is next introduced at the surface into the pipestring, the slurry descending as shown by reference to FIG. 3, throughpipe 18 via the outer tubular member 11, and through the annulus betweenouter tubular member 11 and inner tubular member 12. The water-gravelslurry is discharged from the lower terminal end of outer tubular member11, the gravel being deflected radially outwardly by contact with theupper end of tubular fitting 15, gravitating downwardly and being spreadabout the circumference of screen 17 filling the annulus between theouter surface of screen 17 and the casing forming a wall inside the well16.

As the gravel is accumulated about the screen 17, within the annulusbetween the outer surface of the screen 17 and the casing of the well16, the water separates therefrom and enters into the screen 17 via theperforated surface thereof and ascends, as shown by specific referenceto FIG. 4, through the tubular fitting 15, passes through the checkvalve 14, and enters into the axial opening through inner tubular member12. The water passes upwardly through inner tubular member 12 andegresses therefrom via the upper opening 12,, 12 after which time itascends to the surface via the annulus formed between the productiontubing 8 and pipe 18 and the drill pipe string which lies within thecasing of the well 16.

In the practice of packing a well, an amount of gravel approximately ornearly equal in amount to that required to pack the annulus between theouter face of the screen 17 and the casing of the well 16 is measuredout, and slurried in water, and the slurry then pumped downwardlythrough the drill pipe string. In the operation, when the gravel hasfilled the annulus, pressure builds up and back pressure indicates thatthe gravel has reached the tool, this occurring perhaps at a pressureranging from about 800 to about 1000 psig, or higher, this providing atight, secure pack.

The annulus between screen 17 and the casing of the well 16 thus packed,the drill pipe string is next rotated counterclockwise to uncoupled thewell gravelling tool 10 from the union 20 of screen 17. The assemblycomprised of a drill pipe string, inclusive of pipe 18, and wellgravelling tool 10 is then withdrawn to the surface and the operationrepeated ad infinitum until the packing of the well is completed.

It is apparent-that various modifications and changes, such as inabsolute or relative dimensions of the parts, materials and componentsof the well gravelling tool can be made without departing the spirit andscope of the invention as will be apparent to those skilled in the art.

The top] of this invention can be used to pack through. 'e.g., 2 inchestubing to any size casing available for use in well completion.

Having described the invention, what is claimed is:

1. Apparatus characterized as a well gravelling tool for operativeattachment to the terminal end of va drill pipe string for use, withproduction tubing, in the conveyance, positioning and gravel packing ofa tubular member within a well via use of a water-gravel slurry which.in combination, comprises:

a pair of concentric tubular members,

a large diameter single wall tubular member with means located at theenclosing upper wall thereof for operative engagement and opencommunication with the lower wall end of a pipe at the terminus of adrill pipe string.

a small diameter tubular member mounted within said large diametertubular member, the upper end of which is permanently opened through thewall of the large diameter tubular member to the exterior and closed tothe opening through the large diameter tubular member,

a fixed elastic seal of tubular shape externally fitted upon the largediameter single wall member for tight engagement with the productiontubing within which the apparatus is conveyed,

means located on the lower extremity of said small diameter tubularmember for operative engagement with the upper end of the tubular memberpositioned in the well,

whereby the apparatus can be conveyed via the production tubing into thewell, a water-gravel slurry can be passed downwardly from the surfacethrough the drill pipe string, through the large diameter tubularmember, and the annulus between the pair of concentric membersconstituting the well gravelling tool, and gravel dispersed and packedunder pressure about the annulus of the tubular member positioned in thewell, water passed through the packing into the positioned tubularmember and upwardly through the opening of the small diameter tubularmember, and into an annulus formed by the outer wall of the pipesconstituting the drill pipe string where it ascends to the surface. theapparatus detached from the tubular member now in place, and the drillpipe string and apparatus returned without any necessity of withdrawingthe production tubing.

2. The apparatus of claim 1 wherein the upper terminal end of the largediameter tubular member is threaded for operative engagement to thelower terminal end of the drill string, and the lower terminal end ofthe tubular element is threaded with threads of opposite cast forengagement with the upper end of the tubular member positioned withinthe well.

3. The apparatus of claim 2 wherein the threads of the large diametertubular member are right hand threads, and those on the lower terminalend of the tubular element are left hand threads.

4. The apparatus of claim 1 wherein the upper terminal end of the largediameter tubular member is of reduced cross-sectional diameter andexternally threaded, the small diameter tubular member concentricallymounted therein is bifurcated at the top such that the terminal endsthereof which provide openings which extend to the exterior are about180 apart and the lower end thereof extends beyond the confines of theterminal end of the large diameter tubular member.

5. The apparatus of claim 1 wherein the lower terminal end of the largediameter tubular member is provided with a.lip within which the tubularelastic seal is circumferentially seated.

6. The apparatus of claim 1 wherein a check valve is located upon andoperatively communicated with the opening through the small diametertubular member, the opening through small tubular member permittingupward flow but not the downward flow of water, and the means located onthe small diameter tubular member at the lower extremity of said toolcomprises a tu bular element.

7. The apparatus of claim 6 wherein the upper end of the tubular elementlocated below the check valve and on the lower extemity of said smalldiameter tubular member is of frusto-conic shape with the tapered endfaced upwardly, and the opposite lower end thereof is threaded.

8. The apparatus of claim 7 wherein the lower end of said member isprovided with left hand threads.

9. The apparatus of claim 7 wherein the outer larger diameter sides ofthe straight side portion of said member is provided with a plurality ofspaced apart longitudinally oriented grooves.

10. The apparatus of claim 9 wherein there are four grooves, each spacedapart one from another.

1. Apparatus characterized as a well gravelling tool for operativeattachment to the terminal end of a drill pipe string for use, withproduction tubing, in the conveyance, positioning and gravel packing ofa tubular member within a well via use of a water-gravel slurry which,in combination, comprises: a pair of concentric tubular members, a largediameter single wall tubular member with means located at the enclosingupper wall thereof for operative engagement and open communication withthe lower wall end of a pipe at the terminus of a drill pipe string. asmall diameter tubular member mounted within said large diameter tubularmember, the upper end of which is permanently opened through the wall ofthe large diameter tubular member to the exterior and closed to theopening through the large diameter tubular member, a fixed elastic sealof tubular shape externally fitted upon the large diameter single wallmember for tight engagement with the production tubing within which theapparatus is conveyed, means located on the lower extremity of saidsmall diameter tubular member for operative engagement with the upperend of the tubular member positioned in the well, whereby the apparatuscan be conveyed via the production tubing into the well, a water-gravelslurry can be passed downwardly from the surface through the drill pipestring, through the large diameter tubular member, and the annulusbetween the pair of concentric members constituting the well gravellingtool, and gravel dispersed and packed under pressure about the annulusof the tubular member positioned in the well, water passed through thepacking into the positioned tubular member and upwardly through theopening of the small diameter tubular member, and into an annulus formedby the outer wall of the pipes constituting the drill pipe string whereit ascends to the surface, the apparatus detached from the tubularmember now in place, and the drill pipe string and apparatus returnedwithout any necessity of withdrawing the production tubing.
 2. Theapparatus of claim 1 wherein the upper terminal end of the largediameter tubular member is threaded for operative engagement to thelower terminal end of the drill string, and the lower terminal end ofthe tubular element is threaded with threads of opposite cast forengagement with the upper end of the tubular member positioned withinthe well.
 3. The apparatus of claim 2 wherein the threads of the largediameter tubular member are right hand threads, and those on the lowerterminal end of the tubular element are left hand threads.
 4. Theapparatus of claim 1 wherein the upper terminal end of the largediameter tubular member is of reduced cross-sectional diameter andexternally threaded, the small diameter tubular member concentricallymounted therein is bifurcated at the top such that the terminal endsthereof which provide openings which extend to the exterior are about180* apart and the lower end thereof extends beyond the confines of theterminal end of the large diameter tubular member.
 5. The apparatus ofclaim 1 wherein the lower terminal end of the large diameter tubularmember is provided with a lip within which the tubular elastic seal iscircumferentially seated.
 6. The apparatus of claim 1 wherein a checkvalve is located upon and operatively communicated with the openingthrough the small diameter tubular member, the opening through smalltubular member permitting upward flow but not the downward flow ofwater, and the means located on the small diameter tubular member at thelower extremity of said tool comprises a tubular element.
 7. Theapparatus of claim 6 wherein the upper end of the tubular elementlocated below the check valve and on the lower extemity of said smalldiameter tubular member is of frusto-conic shape with the tapered endfaced upwardly, and the opposite lower end thereof is threaded.
 8. Theapparatus of claim 7 wherein the lower end of said member is providedwith left hand threads.
 9. The apparatus of claim 7 wherein the outerlarger diameter sides of the straight side portion of said member isprovided with a plurality of spaced apart longitudinally orientedgrooves.
 10. The apparatus of claim 9 wherein there are four grooves,each spaced 90* apart one from another.